1. Field of the Invention
The present invention relates generally to electrical devices, and particularly to electrical devices having safety shutters.
2. Technical Background
Electric service is provided in a structure by installing electric circuits throughout the structure. Each electric circuit includes electrical wiring that interconnects various kinds of electrical wiring devices that are disposed at various locations throughout a structure depending on the electrical design. Most people are familiar with electrical wiring devices such as outlet receptacles, light switches, dimmers, ground fault circuit interrupters, and the like. For example, duplex outlet receptacles are typically installed in wall mounted device boxes. After they are properly terminated to the electrical wiring, a cover plate is installed over the outlet receptacle and the device wall box to “complete the enclosure” and installation. The term “completing the enclosure” means that no energized wires or electrical conductors are accessible to a user. Receptacles are not only found in electrical wiring devices but in other electrical devices as well such as appliances, raceways, multiple outlet strips, power taps and extension cords.
Receptacles are often associated with protective devices such as ground fault circuit interrupters (GFCIs), transient voltage surge suppressors (TVSS) and arc fault circuit interrupters (AFCIs) are examples of electrical protective devices because, as their name suggests, they are used to protect persons and structures from being harmed by electrical fault conditions. Protective devices are typically equipped with a set of interrupting contacts that are used to break the connection between the line terminals and load terminals when the protective device detects a fault condition. Stated differently, the line/load electrical connection is broken to interrupt the load circuit and thereby remove the fault condition.
Electrical devices have line terminals for connecting the device to a source of AC power, and load terminals for connecting the device to an electrical load (or the electrical wiring that is connected to the load). Line terminals are configured to interface with upstream wires or receptacles to provide power to the electrical device from the AC power source. There are two kinds of load terminals in electrical devices: receptacle load terminals, and feed-thru load terminals. The receptacle load terminals are contact structures that are configured to accept and pinch the blades of a plug that is inserted therebetween to provide power to the load. Feed-thru terminals, on the other hand, are configured to terminate wires which are connected to one or more electrical devices that are downstream from the electrical device. A branch electric circuit of an electrical distribution system often includes a string of downstream receptacles.
One safety issue that has been problematic for parents and other caregivers relates to the danger of shock or electrocution of young children. Toddlers and young children seem to have a propensity of inserting objects such as paper clips, screwdriver blades and other such things into the receptacle contact openings. Unfortunately, this scenario often results in an electric shock, burns, or electrocution. In one approach that has been considered, electrical receptacles are equipped with shuttered openings that prevent foreign objects that are inserted into the receptacle openings from touching the live receptacle contacts within. However, many related art designs are ineffective because these shutters often operate if the child manages to simultaneously place an object in the hot and neutral openings. What is needed is a shutter mechanism that only opens when an actual plug is being inserted into the receptacle.
In one approach that has been considered, the related art shutters are overly complex because they comprise multiple parts and spring elements that are not integrated into a unitary sub-assembly. Many of these related art shutters have a housing that includes the moving shutter components. This approach has a drawback in that the housing adds to the bulk and thickness of the shutter assembly. The cost and time of assembling the shutter mechanism make these designs unattractive. Further, automated environments often generate vibrations and mechanical forces that tend to introduce failure modes.
The shutter assemblies briefly discussed above are typically not appropriate for 15/20 A devices. Those skilled in the art will understand that in a 15 A plug blade set, the hot blade is parallel with the neutral blade. However, in a 20 A plug blade set the neutral blade is perpendicular to the hot blade. Thus, combination 15 A/20 A devices typically employ a neutral opening T-slot that accommodates both types of plug blade sets.
In yet another approach that has been considered, a shutter assembly has been considered that eliminates the shutter housing. The shutter assembly includes a lower shutter member that accommodates an upper shutter member there within. A spring is disposed between the upper and lower shutter members such that the spring force urges the shutter members apart to maintain the shutters in a closed state. For 20 A or 15 A/20 A receptacles, an additional shutter is accommodated within the lower shutter member. One drawback associated with this arrangement is that the upper shutter may become skewed within the bottom shutter. When this occurs, the shutter assembly movement between the open and closed position becomes compromised. In addition if the insertion of the plug blade is too forceful, the shutter assembly may be permanently fixed in the open state. What is needed is a shutter assembly that addresses these issues in a reliable manner. Moreover, if the shutter assembly under consideration is adapted for 15 A/20 A use, the application of a few pounds of force with, e.g., a screw driver, may be enough to drive a shutter protecting the T-slot opening into the open position.
What is needed is a shutter assembly that addresses the drawbacks and reliability issues described above. Moreover, a shutter assembly is needed that is suitable for 15 A, 15/20 A or 20 A use. A 15/20 A shutter assembly is needed that maintains the shutters in a closed position even when excessive force is applied to them.